Converting system



June 21, 1938. F. E. BLOUNT 2,120,972

CONVERTING SYSTEM Filed Sept. I 11, 1935 GAS FILLED 0A5 FILLED 35 6.45FILLED FIG? FILLED FILLED FIGS FILLED GAS FILLED FIG. 4

FILLED IN l/E/V TOR F E. BL OUNT ATTORNEY Patented June 21, 1938 UNiTED'STATES PATENT OFFICE Telephone Laboratories,

Incorporated, New

York, N. Y., a corporation of New York Application September 8 Claims.

This invention relates to converting systems and more particularly to asystem for converting direct current into alternating current.

An object of this invention is to convert direct current intoalternating current efficiently and economically.

A more particular object of this invention is to produce from a directcurrent an alternating current, the frequency of which is independent ofload conditions of a system.

Many systems have been proposed for the conversion of direct currentinto alternating current. Some of these systems involve the use ofmoving mechanical parts, while others employ vapor valves or gaseousspace discharge devices. The frequency of the alternating currentproduced by most systems of this latter type is dependent upon the loadcondition. Since the load characteristic varies over a period of time,the frequency of the alternating current produced by these systems alsochanges. In telephone communication systems the production from a directcurrent source of an alternating current, the frequency of which issubstantially constant, is desirable for ringing purposes.

In accordance with a feature of this invention, an alternating currentwhich is of substantially constant frequency and independent of loadconditions is derived from a direct current. The direct current isconverted into an alternating current by the periodic discharges of acondenser which cause the alternate ionization of two gaseous spacedischarge devices.

In accordance with another feature of this 35 invention, a circuit iscontrolled by the periodic discharge of a condenser through a relay. Thecircuit may be closed or opened at different predetermined periods.

In a specific embodiment, the direct current is converted into analternating current by the periodic discharge of a condenser through agaseous valve. The electromotive force resulting from the discharge isimpressed on the control electrodes of two gaseous space dischargedevices. Only one of the devices is in a condition to ionize. Thecurrent resulting from the ionization of the device comprises one pulseor half cycle of the alternating current. After the passage of apredetermined interval the condenser again discharges through thegaseous valve and the other device is ionized. The ionization of thesecond device causes the interruption of the current traversing thedevice previously ionized. The repetition of this cycle of operationincluding the periodic ionization of the two devices 11, 1935, SerialNo. 40,087

results in the production of an alternating current.

A more comprehensive understanding of this invention may be obtained byreference to the accompanying drawing in which:

Fig. 1 is a schematic diagram of a simple embodiment of this inventioninvolving the use of gaseous space discharge devices of the hotcathodetype.

Fig. 2 shows schematically an embodiment of this invention in whichcold-cathode space discharge devices are employed.

Fig. 3 illustrates an interrupter circuit in accordance with thisinvention.

Fig. 4 shows schematically a modification of the interrupter circuitillustrated in Fig. 3.

In Fig. 1, two space discharge devices I and 2 are connected inpush-pull relation. The devices I and 2 are filled with a gaseous mediumsuch as neon, comprise three electrodes, anode, cathode and controlelectrodes, and are of the type known in the art as heated cathodegaseous space discharge devices. The grids of devices I and 2 arenormally negatively biased by means of a source 3 to prevent breakdownof these devices. The source 3 is connected to the control electrodes ofdevices I and 2 through the secondary winding 4 of a transformer 5 andthrough resistances 6 and I, respectively. Heating current for thecathodes of devices I and 2 is supplied by a source 8.

One terminal of the primary winding of a transformer 9 is connected tothe anode of space discharge device I, while the other terminal of theprimary winding of transformer 9 is connected to the anode of device 2through the armature and make contact of a relay IS. The secondarywinding of the transformer 9 is connected to the output circuit 20. Acondenser I0 is bridged across the terminals of the primary winding oftransformer 9. The mid-point of the primary winding of transformer 9 isconnected to one terminal of the primary winding II of the transformer5. The positive terminal of a direct current generator I2 is alsoconnected to the midpoint of the primary winding of the transformer 9.The negative terminal of the direct current generator I2 is associatedwith the other terminal of the primary winding II through a seriesconnection including an armature and make contact of a relay I3, aresistance It and a two-element gaseous space discharge device 2I. Thedevice 2I is a gas-filled ionic discharge device which does not conductcurrent until a certain critical potential is attained. The gas ionizesat this critical potential and the potential across the electrodes ofthe device drops to approximately the restoral value of the device. Therestoral value is substantially independent of the current flowingthrough the device. When a condenser is discharged through the device 2|and the inductance comprising the winding II, the inertia due to theinductance reduces the potential across the device to a value below thatrequired for ionization and the device ceases to conduct current. Thenegative terminal of the generator I2 is also connected to the cathodesof devices I and 2 through an armature and make contact of relay I3. Acondenser I5 is connected between the mid-point of the primary windingof transformer 9 and the common conmeeting point of resistance I4 anddevice 2|. Energizing current is supplied for the relay I3 by a sourceI6 through a manually operated switch I I. When the armature and makecontact of relay I3 engage to connect the cathodes of devices I and 2 tothe negative terminal of generator I2, anode potential for device I issupplied by the direct current generator I2 through a portion of theprimary winding of transformer 9, while anode potential is supplied tothe device 2 from the generator I2 through a portion of the primarywinding of transformer 9 and the armature and make contact of the relayI8. The armature of relay I8 is of the type which is slow in engagingwith its associated make contact. A battery I9 furnishes energizingcurrent for the relay I8 through an armature and make contact of relayI3.

The system shown in Fig. l. is started by closing manually the switchIT. The closing of switch I! completes a circuit from ground throughswitch H to relay I3 and battery !5 to ground resulting in theenergization of relay I3. The energization of relay I3 causes theengagement of the armatures and make contacts of that relay to completecircuits for the energization of relay I8 and to charge condenser I5through resistance I4. The engagement of the armature and make contactof the relay I3 to charge condenser I5 also results in the supply ofanode potential from the generator I2 to the device I. The biasfurnished by the source 3 is, however, of such value that the device Idoes not operate at the potential applied to the anode cathode circuitby the generator I2. The secondary winding 4 of the transformer 5 iswound and is connected in the input circuit of devices I and 2 in such adirection that the high voltage surge generated in the primary windingII opposes the potential impressed by the source 3. The condenser I5charges through the resistance I4 with current supplied by generator I2.When the potential across the condenser I5 attains a value equal to thatof the operating potential of device 2i, the device 2I ionizes to permitcondenser I5 to discharge. When this discharge occurs a voltage of shortduration is generated in the primary winding II of transformer 5. Thefrequency of these pulses is controlled by the values of the resistanceI4 and of the capacity of condenser I5. The surge generated in thewinding 4 is sufllcient to overcome the negative bias furnished bysource 3 to operate the device I. Current flowing in the anode-cathodecircuit of device I reduces the potential of the anode and of the plateof the condenser Ill connected to it to a point equal to the internaldrop in the device l. Relay I8 which is slow in operating is actuated atthis time and closes the anode circuit of device 2. The potential at theanode of device 2 and the plate of the condenser I connected to it isthat of the input electromotive force or that generated by the generatorI2. The next surge resulting from the discharge through device 2| causesdevice 2 to operate. The potential at the anode of device 2 quicklyfalls to a value corresponding to the internal drop of device 2. Theplate of the condenser I0 connected to the anode of device 2 assumes thesame potential. With the operation of the device 2, the charge drawnfrom the condenser causes the potential of the opposite plate which isconnected to the anode of device I to be reduced below the restoralvalue for device I and device I ceases to operate. The potential of theanode of device I gradually increases to the value of the input voltageas the condenser I0 recharges. When the next pulse is impressed on thecontrol electrode of devices I and 2, device I is ionized, while device2 ceases to operate. The impulse of current resulting from the alternateionization of devices I and 2 with the resulting passage of currentthrough the primary of transformer 9, induces an alternating voltage inthe secondary thereof and alternating current flows in the outputcircuit 20. After the production of the first cycle of alternatingcurrent and as long as the switch I'I remains closed, the relays I3 andI8 function no further in the operation of the system other than theyare continually energized to insure connection of the source I2 to theanode-cathode circuits of devices I and 2.

Fig. 2 shows an inverter circuit similar to that of Fig. 1 except thatgaseous space discharge devices known commercially as the cold cathodetype are employed instead of the hot cathode type shown in Fig. 1. Twodevices 22 and 23 known commercially as the cold cathode three-elementtype of gaseous discharge devices are connected in push-pull relation ina manner similar to that of the devices I and 2, respectively, shown inFig. l. The device 22 comprises two cathodes 35 and 3S and an anode 31,and the device 23 comprises two cathodes 35 and 36 and an anode El. Thecathodes 36 and 36 are connected by the arma-a ture and make contact ofrelay I3 to the negative terminal of the generator I2 in a mannersimilar to the connection of the cathodes of devices I and 2 shown inFig. l. The cathodes 35 and 35' are serially connected throughresistances 6 and 1 respectively to a terminal of the secondheating thecathodes of the devices 22 and 2a is necessary, the source 8 iseliminated from the system shown in Fig. 2. In all other respects thesystem shown in Fig. 2 is the same as that shown in Fig. 1 except that asource of biasing potential, such as the battery 3 in Fig. 1, has beenomitted. Such a source may or may not be employed depending upon theionization potential of the devices 22 and 23 and the magnitude of thepotentials induced in the secondary winding of the transformer 5.

Operation of the system shown in Fig. 2 is started by closing switch Hwhich connects the positive terminal of the generator I2 to the anodecircuit of device 22 and the circuit comprising resistance I4 andcapacitance I5. current flows in the anode circuit of device 22 untilthe gas is ionized by the potential impressed across the two cathodes 35and 36 of that device.- When the potential across condenser I issurficient to ionize device 2 I, a surge of current passes However, no Fthrough the primary winding II of transformer 5. The electromotive forceinduced in the secondary winding 4 ionizes the gas in the device 22 topermit current to flow from the anode to the cathodes. Current flowingin the anode-cathode circuit of device 22 and to the plate of thecondenser IIJ connected to the anode 31 is reduced in potential toapoint equal to the internal drop of the device 22. .Relay I8 operatesat this time to close the anode circuit of device 23. The surgeresulting from impulse of current through device 2I and the consequentelectromotive force induced in the secondary winding 4 causes the gas indevice 23 to ionize by the potential impressed across the cathodes 35and 36 and to permit current to flow in its anode circuit. The currentflowing in the anode cathode circuit of device 23 reduces the potentialof the plate of the condenser Ill connected to the anode 31' of device23. When this reduction of potential occurs, the potential of theopposite plate which is connected to the anode 3'! of device 22 isreduced below the restoral value for the device 22 and the device 22ceases to operate. The potential of the anode of device 22 graduallyincreases to a value of the input voltage as the condenser I9 recharges.When the next pulse is impressed on the input circuit of devices 22 and23 as a result of the discharge through the device 2I, device 22- isionized and the discharge through device 23 is extinguished. Analternating electromotive force is thereby generated in the outputcircuit 20.

In Fig. 3 an interrupter circuit is shown. The circuit illustrated inFig. 3 is the same as that shown in Fig. 2 except that instead of atransformer 9 connected in the output circuit of devices 22 and 23, arelay 24 is connected in the output of device 22 and a relay 25 in theoutput of device 23. In addition, the circuit shown in Fig. 3 differsfrom that shown in Fig. 2 in that instead of resistance I4, tworesistances 28 and 29 in series are employed through which the condenserI5 is charged. An armature and its associated make contact 39 of therelay 24 are bridged across the resistance 29 so that the engagement ofthis armature and make contact results in substantially removing theresistance 29 from the system. When the relay 24 is energized to engagethe armature and make contact 30, the condenser I5 is chargedsubstantially through the resistance 28, the resistance of the lineassociated with armature and make contact 30 being negligible. Since thetime interval between the operation of the device 2I is determined bythe values of condenser I5 and resistance 28 or resistances 28 and 29,the energization of relay 24 causes a difference in the intervalelapsing after the last discharge of the device 2|. This feature of theinterrupter circuit is of advantage in that interruption of twodifferent periods may be obtained.

The desired interruption is obtained by the engagement and disengagementof the armature and make contact associated with relays 24 and 25. Inaddition to the armature and make contact 39, another armature and makecontact 3|- of relay 24 is associated with a circuit 23 while anarmature and make contact associated with relay 25, closes and opens acircuit 21. The parts of the system, the operation and function of whichare the same as those shown in Fig. 2 have the same numerals in Fig. 3.

The operation of the system shown in Fig. 3 is substantially the same inprinciple as that shown in Fig. 2. After the switch I! is operatedmanually, the condenser I5 commences to. charge through resistances 28and 29. When the potential of the condenser I5 attains a valuesufficient to break down the device 2I, the resulting discharge currentimpulse through device 2I operates to induce a surge through secondarywinding 4 of transformer 5. Device 22 is ionized as a result of thissurge to energize relay 24. The engagement of the armatures and makecontacts3l and 30 closes the circuit 26 and effectively removes theresistance 29 from the system, respectively. At this time the armatureand make contact of relay I8 engage to connect the direct current sourceI2 to the anode cathode circuit of device 23. Immediately afterdischarge of the condenser I5 through the device 2I, the condenser I5commences to charge through resistance 28. Since the resistance 29 iseffectively removed from the charging circuit, the time between thecommencement of charge of the condenser and the discharge thereof isdetermined by the values of resistance 28 and condenser I5. When thepotential of the condenser I 5 attains that of the breakdown of device 2I, a surge is induced in the winding 4. The device 23 is ionized andcurrent flows in the output of device 23 to energize relay 25. Theresulting engagement of armature and make contact 32 closes the circuit21. For the reasons stated in the description of Fig. 1, current throughdevice 22 is extinguished. Relay 24 is as a result deenergized. Thearmatures and make contacts 30 and 3| are disengaged, the former toeffectively restore the resistance 29 to the charging circuit, while thelatter effects the breaking of the circuit 26. Condenser I5 is nowcharged from the direct current source through resistances 28 and 29.After a period elapses, depending upon the time constants of resistances28 and 29 and condenser I5, the device 2I is again ionized to break downthe impedance of device 22 in turn. The operation is repeated asdescribed above. Of course, after the first cycle of operation and aslong as the switch I'i remains closed, the relays I3 and I8 do notfurther influence the functioning of the system. The devices 22 and 23then continue to ionize alternately and to permit current to flowthrough them from the direct current source I2.

It may be observed that in the system shown in Fig. 3, the intervalsbetween the ionization of the devices 22 and 23 differ. As a result, theclosing times of circuit 26 and that of circuit 21 also difier. The timeduring which the circuit 21 is closed by armature and make contact 32 isdependent upon the time constants of condenser I5 and resistances 28 and29, while the time during which circuit 26 is closed by armature andmake contact 3| is determined by the time constant of condenser I5 andresistance 28 alone. This difference in time interval is advantageous inmany systems. For example, for signaling purposes in telephonecommunication systems, it is desired. to automatically maintain aringing signal in telephone subscribers sets for approximately twoseconds, having a silence period of four seconds, resuming the ringingsignal for two seconds and continuing this cycle of operation until thetelephone subscriber answers the call. It has been found that if theresistance 28 is 5 megohms, resistance 29-5 megohms, condenser I51.12microfarads, condenser III-10 microfarads and the voltage of thegenerator I2-130 volts the circuit 29 is closed for approximately twoseconds, while the circuit 21 is closed alternately for a period of fourseconds. The signaling apparatus for ringing could then be connected tothe circuit 26 to achieve the purpose desired in these telephonecommunication systems.

Like the interrupter system illustrated in Fig. 3, the system shownschematically in Fig. 4 comprises two gaseous space discharge devices 40and 4|, known commercially as the cold cathode type, connected inpush-pull relation. The device 40 comprises two cathodes 55 and 56 andan anode 51. The device 4| comprises two cathodes 55' and 56 and ananode 51. One plate of a condenser 43 is connected to the cathodes 55and 55 while the other plate of the condenser is connected to the anodes51 and 51 through two resistances 44 and 45. A battery 46 or othersource of unidirectional current furnishes current for charging thecondenser through a manually operated switch 41 and resistance 44 orresistances 44 and 45 and anode potential for devices 40 and 4|. Anelectromagnetic relay 48 is inserted in the output circuit of device 40,while a resistance 49 is serially connected in the output circuit ofdevice 4|. A pair of contacts and an armature 59 associated with theelectromagnetic relay 48 connect the plate of the condenser connected tothe resistances 44 and 45 to either the cathodes 56 or 56'. When therelay 48 is energized the condenser 43 is connected to the cathode 56 ofdevice 4|, while when the relay 48 is not energized, the condenser 43 isconnected to the cathode 55 of the device 40. A make contact andarmature 50 associated with the relay 48 effectively remove theresistance 45 from the charging circuit. Another make contact andarmature 5| controls a circuit 52. A condenser 53 connected to theanodes 51 and 51 of devices 4|! and 4| operates and functions in amanner similar to that of condenser |0 in Figs. 1 to 3.

The system shown in Fig. 4 is started by depressing the key 41 tocomplete the charging circuit for condenser 43 and connects the battery46 to the anode-cathode circuits of devices 48 and 4|. At that time, therelay 48 being deenergized, the condenser 43 charges through resistances44 and 45. Further, the condenser is connected to the cathode 56 ofdevice 40. When the condenser attains a potential above that at whichthe device 40 breaks down, the device 40 ionizes. The relay 48 isenergized to switch the condenser from the cathode 56 of device 40 tothe cathode 55 of device 4| to effectively remove the resistance 45 fromthe charging circuit and to close the circuit 52. The condenser 43 nowcommences to charge through resistance 44. When the condenser 43 attainsa sufilcient potential, the device 4| ionizes. For the reasons stated inthe description of Figs. 2 and 3, the condenser 53, like the condenserID in Figs. 2 and 3, operates at this time to interrupt the currenttraversing device 40. No current flows in the output of device 40 andrelay 48 is deenergized. The condenser 43 is switched from the cathode56' of device 4| to the cathode 56 of device 40. Resistance 45 isinserted in the charging circuit and the current flowing through thecircuit 52 is interrupted. This cycle of operation is repeated wherebythe circuit 52 is closed and opened at predetermined intervals. Theperiod during which the circuit 52 is closed is determined substantiallyby the time constants of resistance 44 and the capacity of condenser 43,while the period during which the circuit 52 is opened is determined bythe time constants of condenser 43 and resistances 44 and 45.Accordingly, the lengthening or shortening of the period of closure ofthe circuit 52 may be controlled by increasing or decreasing the valuesof resistances 44 and 45.

While preferred embodiments of this invention have been illustrated anddescribed, various modifications therein may be made without departingfrom the scope of the appended claims.

What is claimed is:

1. A system for converting direct current into alternating currentcomprising a plurality of gaseous space discharge devices connected inpush-pull relation, means for impressing an operating potentialsuccessively to the anodes of said devices, and a circuit coupled to theinput circuit of said devices comprising a capacitance, a source ofdirect current for charging said capacitance and a gaseous spacedischarge device for discharging said capacitance to break downsuccessively said plurality of gaseous space discharge devices.

2. In combination, a pair of gaseous discharge devices, output circuitsfor said devices, means for applying a substantially constant directcurrent operating potential to the output circuit of one of saiddevices, means for applying an equal substantially constant directcurrent operating potential to the output circuit of the other of saiddevices a predetermined interval after the application of operatingpotential to said first output circuit, means for ionizing said devicesalternately, and means responsive to the ionization of said other devicefor deionizing said first device.

3. A circuit interrupting system comprising two circuits, two spacedischarge devices having input and output circuits connected thereto, athird gaseous space discharge device in the input circuits of saiddevices, means including a capacitance and a resistance for renderingconductive at predetermined intervals said third device, means in saidoutput circuits for rendering conductive said two devices alternately inresponse to the conductivity of said third device, a relay in the outputcircuit of each of said two devices and responsive to the conductivityof its associated device, and a circuit controlled by the actuation ofeach of said relays.

4. In combination, a pair of gaseous space discharge devices each havinga cathode, an anode and a control electrode, an output circuit coupledto the anodes of said devices including means for impressing a directcurrent positive potential to said anodes with respect to the cathodesof said devices, a control circuit connected to the control electrodesof said devices and including means for applying a bias to said controlelectrodes sufficient to hold said devices non-conductive, and means forovercoming said bias intermittently to initiate ionization of saiddevices including an electric discharge device coupled to said controlcircuit, a condenser in parallel with said electric discharge device andmeans for charging said condenser.

5. An inverter system comprising a pair of gaseous space dischargedevices connected in push-pull relation, each of said devices having acathode, an anode and a control electrode, a source for applying adirect current positive potential between the cathode and anode of eachof said devices, a condenser connected between the anodes of saiddevices, and means for applying a starting potential alternately to thecontrol electrodes of said devices including a gaseous discharge devicecoupled to the control electrodes of said first devices and a condenserin parallel with said source and said last-mentioned device.

6. An inverter system comprising a pair of gaseous space dischargedevices: each having a cathode, an anode and a control electrode, anoutput circuit connected between the anodes of said devices, a controlcircuit connected between the control electrodes of said devices, acondenser connected between said anodes, means including a directcurrent source for impressing a potential between the cathode and anodeof one of said devices, means including said source for impressing apotential between the cathode and anode of the other of said devices apredetermined interval after the impressing of said first potential, andmeans coupled to said control circuit for intermittently impressing astarting potential thereon including a condenser in circuit with saidsource and chargeable thereby and means for discharging said condenserat periodic intervals.

7. An inverter system comprising a pair of gaseous space dischargedevices each having a cathode, an anode and a control electrode, controland output circuits for said devices, means including a direct currentsource for applying a potential, sufiicient to sustain ionization ofsaid devices, to the anodes of said devices, a condenser connectedbetween said anodes, and

means for impressing intermittently a potential upon said controlcircuit to initiate ionization of said devices alternately including acondenser coupled to said control circuit and in shunt with said sourceand a gaseous space discharge device for discharging said secondcondenser at periodic intervals.

8. In combination, an electric discharge device having a cathode, ananode and a control electrode, an output circuit connected between saidanode and said cathode including a direct current source for applying anoperating potential between said cathode and said anode, means forperiodically decreasing said potential below a value sufficient tosustain ionization of said device including a condenser and aunidirectional conductive device connected between said cathode and saidanode, a control circuit connected between said cathode and said controlelectrode, and means for intermittently impressing a starting potentialupon said control circuit including a condenser coupled to said controlcircuit and directly in series with said source and adapted to becharged thereby and means for periodically discharging said secondcondenser.

FRANK E. BLOUNT.

